Piston



June 4, 1940. R, c CRQSS 2,203,455

PISTON Filed Oct. 4. 1938 I Patented June4, 1940 i Q t i J l 1 UNI ED "STATES rarest orries Application October 4, 1938; SerialNo; 233,276

In Great Britain October-12, 1937 ,1 Claim (Cl. 309-) t This invention relates to pistons for internal machined accurately to a uniform radial depth; combustion engines; pumps and the like andhas Each of these grooves is fitted with a piston i for its object to *providean improved piston fitted ring (shown at 3 in Figures 2, 3, 4 and 5) whose with piston rings arranged to take the bearing radial thicknessis made slightly greater than 5 load of the pistonandto act as cushioning memthe radial depth of, thegroove 2 so that the 5 bers to preventpi'ston slap. Theinvention is ring takes the bearing" load and prevents the particularly applicable to engines or machines piston l fromrubbing directly against the walls in which both" piston and cylinder are made of of thecylinder: For an 80 mm. cylinder bore aluminum alloy so that somesort of bearing ring using rings of one-sixteenth inch' square wire, a

is essential to prevent the alloy piston from rubring clearanceof from six to ten thousandths of 10 bing against the alloy cylinder. The invention an inch-has been found suitable (i. e., the amount may also be applied with advantage, however; 'by which the radial thickness of the wire exceeds to pistons workingin cast iron' cylinders or cylthe depth ofgroove. Accordingto the preferred inders fitted withhard liners of such a nature method of fitting, the pistonis first fitted to 16 that the preventionof direct rubbing contact the cylinder inthe ordinaryway asrequired for between piston and cylinder is not ordinarily a piston required tobear directly against the essential. walls of the cylinder as usual, and is then formed In the manufacture of pistons according to the with grooves 2 having a radial depth exactly present invention, advantage is taken of the equal to the radial thickness of the wire rings 3.

20 fact that a piston ring made by winding and About six to ten thousandths of an inch is then 20 bending a drawn metal wire, such as upon a skimmed off the cylindrical walls of the piston mandrel or otherwise, is more uniform in thickall round thus p vid the rin clearance ness than a piston ring made in the ordinary hereinbefore referred to. way by turning, grinding or other machining As previously mentioned the uniformity of processes, although it is not so accurately cirthickness of the drawn wire from which the rings 25 cular as a machined ring but inevitably shows 3 are made is extremely accurate. Owing to their some slight departures from the circular shape. method of formation however, the rings are not According to this invention, these properties strictly circular but have irregularities or deare utilised to prevent piston slap by providing partures from the strictly circular form which a piston with two or more unmachined rings are illustrated in much exaggerated form in 30 made by winding and bending drawn metal wire, Figures 2, 3, 4 and 5 of the drawing. Owing to the rings being each mounted in a groove having these irregularities the rings bear against the a radial depth smaller than the radial thickness bottoms of the grooves 2 at certain points as of its ring, and being resiliently compressible indicated at a in the drawing whilst at other therein, so that the drawn wire rings support points they bear against the Walls of the cylinder 35 the bearing load and further have a cushioning as indicated at b. If the piston is thrust against action due to the slight irregularities of contour the wall of the cylinder in the directon of the of the rings due to their method of manufacture. arrow marked as in Figures 3, 4 and 5, so that Theinvention will be more readily understood the piston is displaced from the concentric posifrom the following description with reference to tion shown in Figure 3 to the slightly off-set the accompanying drawing, in whichposition illustrated in Figure 4 the ring 3 shown Figure 1 is a sectional view of a piston made in these figures is bent and therefore offers a according to the invention but with the piston resilient resistance to the displacement of the rings removed to show the grooves more clearly; piston. The wire ring 3 acts as a beam supported Figure 2 is a section through piston and cylinagainst the cylinder walls at the points b and 45 der showing the manner in which the drawn taking the thrust of the piston at the point a. wire ring takes the bearing load, the clearance As the wire ring 3 is deflected by the lateral and the distortion or departure of the piston piston thrust, the points of support 17 move cirring from true circularity being greatly exagcumferentially towards the point a so that the gerated for the purpose of illustration; and resistance to deflection is greatly increased as 5 Figures 3, 4 and 5 are views similar to Figure 2 wil be obvious from inspection of Figures 3 and 4. illustrating the anti-slap cushioning action of In the limit, thelength of wire acting as a beam the rings. would be reduced to zero and the thrust would The piston l shown in Figure 1 has a number be transmitted directlythrough the thickness of of annular grooves 2 of rectangular cross-section the ring 3 as illustrated in Figure 5, The wire 5 ring shown in Figures 3, 4 and 5 will thus resist the piston displacement just described and will tend to restore the piston to its central position. The wire will thus act as a cushion to absorb the thrust momentum and to minimise or we vent piston slap. It will be obvious that, provided a sufiicient number of rings 3 are provided, the irregularities of these rings will provide for a cushioning action similar to that just described in any radial direction, the several rings co-operating to hold the piston 'in a central position and to prevent direct bearing of any part of the piston wall against the cylinder under any normal working conditions.

In order to secure a balanced cushioning action, the wire rings 3 are distributed on either side of the gudgeon pin, the number of rings 3 between the gudgeon pin and the head of the piston being preferably equal to the number between the gudgeon pin and the end of the skirt.

The piston shown in Figure 1 has grooves 2 to receive four wire rings 3 above the gudgeon and four below the gudgeon and two of these grooves are positioned so that they break into the gudgeon pin hole as shown. When only two rings such as 3 are employed, it would be advantageous to locate one above and one below the gudgeon, but it is preferred to employ two or more rings 3 on each side of the gudgeon.

The head of the piston is provided with a further groove 4 to receive a ring (not shown) which may be a floating cast iron piston ring of ordinary construction conventionally designed to form a gas and oil seal. More than one ordinary ring may be used to suitable locations. A groove 5 to receive a scraper ring is also provided in the skirt of the piston. I

In the production of the rings 3, the first step consists in drawing a wire of the required section. This wire is then bent into a circular form such as by winding on a cylindrical mandrel of suitable diameter to form the rings. The variation from true circularity resulting from this method 7 of manufacturing piston rings provides the degree of irregularity necessary for the purpose of the invention. Single rings may be formed on the mandrel of lengths of wire cut to size, or a. wire may be helically wound and the resulting helical spring-like element may be split with a cut to form a plurality of rings in one operation.

"The rings thus formed may be subjected to heat drawn spring steel wire sections bent into an 1 nular non-circular shape, said rings when seated in the grooves of the piston, having the portions which are not true arcs of a circle in relatively non-registering relation vertically of the piston points, said grooves being of a radial depth smaller than the radial thickness of the rings whereby the rings are caused to take the bearing load of the piston in the cylinder.

ROLAND CLAUDE CROSS. 

